A known ink cartridge includes a case including an ink reservoir portion (ink chamber) therein. An ink supply opening and an atmospheric introduction opening are formed through the same side wall of the case. The ink cartridge also includes an ink supply valve configured to selectively open and close the ink supply opening and an atmospheric release valve configured to selectively open and close the atmospheric introduction opening. When the ink supply valve opens the ink supply opening, ink is supplied from the reservoir portion to the outside of case via the ink supply opening. When atmospheric release valve opens the atmospheric introduction opening, the ink reservoir portion is bought into fluid communication with the atmosphere via the atmospheric introduction opening.
Before the ink cartridge is mounted in an image forming apparatus, the pressure in the ink reservoir portion storing ink is less than the atmospheric pressure, and the atmospheric release valve and the ink supply valve are urged by a compression spring, respectively, to close the ink supply opening and the atmospheric introduction opening, respectively, thereby sealing the ink cartridge.
In this ink cartridge, a rod-shaped operation portion for operating the atmospheric release valve protrudes from the inside of the case to the outside of the case through the atmospheric introduction opening.
If the operation portion is erroneously operated such that the atmospheric release valve opens the atmospheric introduction opening when the ink cartridge is transported or is kept in storage, air enters the ink reservoir portion, and the air dissolves into ink. Moreover, if the atmospheric introduction opening is located below the ink reservoir portion while the atmospheric introduction opening is opened by the atmospheric release valve, ink leaks from the ink reservoir portion to the outside of the case through the atmospheric introduction opening.
Therefore, a protection member is attached to the side wall of the case through which the ink supply opening and the atmospheric introduction opening are formed. The protection member has a hole formed therethrough or a recess formed therein to receive the operation portion. The ink cartridge with the protection member attached thereto is then packed in a resin bag, and the interior of the bag is depressurized. Such a known ink cartridge is described in JP-A-2006-142590 for example.
Nevertheless, if air is dissolved in ink stored in the ink reservoir portion when the ink cartridge is mounted to an image recording apparatus and ink is supplied from the ink cartridge to a recording head, the air turns into bubbles in the recording head, which causes clogging of nozzles formed in the recording head, leading to printing failure. In order to prevent this printing failure, deaerated ink is stored in the ink reservoir portion. Moreover, in order to maintain the deaeration of the ink, the pressure in the ink reservoir portion is lowered to be less than the atmospheric pressure.
When the ink cartridge is mounted to the image recording apparatus, if the ink supply valve is operated to open the ink supply opening before the atmospheric release valve is operated to open the atmospheric introduction opening, ink in the nozzles of the recording head is drawn towards the ink cartridge because the pressure in the ink reservoir portion is less than the atmospheric pressure. This breaks the menisci of ink in the nozzles. Therefore, air enters into ink passages formed in the recording head through the nozzles and remains in the ink passages, which leads to printing failure. As a result, maintenance work to restore printing quality is additionally required, which may discard much ink.
Therefore, a user may be instructed to operate the atmospheric release valve to open the atmospheric introduction opening to bring the ink reservoir portion into fluid communication with the atmosphere prior to mounting the ink cartridge to the image recording apparatus. Nevertheless, if the atmospheric introduction opening is located below the ink supply opening when the user holds the ink cartridge in his hand, air introduced via the atmospheric introduction opening may reach the vicinity of the ink supply opening. If the ink cartridge is then mounted to the mounting portion, air bubbles are supplied to the recording head via the ink supply opening, which leads to printing failure.